feat(01-01): add test scaffold, health and static asset tests, fix deprecated APIs

- requirements-dev.txt with pytest and httpx
- tests/conftest.py: client and tmp_data_dir fixtures
- tests/test_health.py: GET /health returns 200 with {"status": "ok"}
- tests/test_static.py: no CDN URLs in templates, dashboard returns 200
- Fix imptune/api/pages.py: use request= kwarg in TemplateResponse (Starlette compat)
- Fix imptune/main.py: replace deprecated on_event with asynccontextmanager lifespan

imptune/api/pages.py

@@ -11,9 +11,9 @@ templates = Jinja2Templates(directory=str(Path(__file__).parent.parent / "templa
 @router.get("/", response_class=HTMLResponse)
 def dashboard(request: Request):
     return templates.TemplateResponse(
-        "dashboard.html",
-        {
-            "request": request,
+        request=request,
+        name="dashboard.html",
+        context={
             "recent_printers": [],
             "recent_packages": [],
         },